Setting Goals/Hitting a moving target

There are a lot of things I'd like to do, though for now the one that I really need to do is live. Since I'm not currently on my own trying to do that, I've got to estimate the cost instead of simply tallying receipts. Of course, the cost of living changes continuously.
So, what sort of information do I have out there? Yeah, I could run around trying to total everything I think I'd need, or I can use someone else's estimates. One estimate that I'm familiar with is the student loan monthly living allowance. It naturally assumes that you'll be living like a student, which is fine with me. As much as I had some bad experiences, people smoking pot and getting me high, people skipping out on rent, utilities not getting paid, the times when things went well were good times. A new one that's recently been introduced to me is what Old Age Security(OAS) and Canada Pension Plan (CPP) will give. I'll have to admit that I don't know how they arrive at the figure. I'm learning about those because my dad recently retired. Finally, there's whatever minimum wage is set at, which is quite livable.
I'm expecting these to cover a bit above what's needed to cover the essentials. Different people will inevitably have a different view on what is essential. When I was going through school, I was well bellow the monthly living allowance. Though I was almost always perpetually short money, but that's another story for another day.

	Source	Amount	Annual
Student monthly living allowance	$897/month	10764
Old Age Security	$502.31/month	6027.72
Guaranteed Income Supplement	$634.02/month	7608.24
Allowance???	$921.00/month	11052
CPP starting at Age 65	$884.58/month	10614.96
Minimum wage at 40 hours a week for 52 weeks	$8.40/hr	17472
Minimum wage at 40 hours a week for 52 weeks with vacation pay	$8.40/hr	18170.88
Minimum wage at 40 hours a week for 52 weeks with vacation pay and 11 stat holidays	$8.40/hr	18910.08

And I quickly begin to question the value of this exercise. If I want to make things even more convoluted, 3.07% of the consumer price index is based off alcohol and tobacco, which I currently do not consume, so should I be able to decrease these figures by 3.07%? Anyway, ball park figure, I'd feel fairly secure if I could get about $10K/a from investments. I'll be really happy if I could pull off $18K/a. Of course that assume no economic down turn, like the one happening to the south of me at the moment.